1. Field of the Invention
The present invention relates to devices adapted to remove slack in endless driven chains and, in particular, to take-up devices for crawler chains used in the mining industry.
2. Description of the Invention Background
In the materials mining industry, such as in the underground mining of coal and similar materials, chain driven continuous mining machines are utilized to remove the coal or ore from the seam. Most continuous mining machines generally have a crawler portion that uses a driven endless crawler or tram chain to propel the mining machine along the mine floor. In addition, endless crawler chains are also utilized on various types of conveyors and haulage vehicles such as mobile articulated conveyors which are used to transport the mined material from the mining machine to other conveyors located remote from the mine face.
The crawler chains used in the operation of those machines generally have a series of crawler pads attached thereto that are adapted to grip the mine floor and propel the mining machine or conveyor forward. The gripping of the mine floor by the crawler pads and the frequent changes in direction of the mining machine or conveyor can cause a significant amount of tensile stresses to build up in the tram chain links. These stresses tend to cause the individual chain links to become slightly elongated which results in the slackening of the endless tram chain around the attending drive and idler sprockets or rollers. To address this problem, take-up devices have been installed on the crawlers in order to increase the distance between the drive and idler sprockets or rollers in such a manner so as to remove the chain slack.
One prior take-up device is illustrated in FIGS. 1-6. As shown in FIGS. 1 and 2, the prior take-up device 200 generally consists of a piston 220 that is rigidly and non-rotatably affixed to the nose piece 215 of a crawler 212. In this design, the piston 220 is slidably received in a sprocket or roller carrying assembly 250 that is slidably received in a slot 216 located in the crawler nose piece 215.
As illustrated in FIG. 4, the sprocket or roller carrying assembly 250 has a counterbore 270 therein that is adapted to receive piston 220. Sprocket or roller carrying assembly 250 additionally has an aperture 251 extending therethrough perpendicularly to the counterbore 270 that is adapted to rotatably receive an axle 252. Idler sprockets or rollers 256, for supporting the tram chain 258, are removably attached to each end of the axle 252.
As can be seen in FIGS. 3 and 4, a grease passage 273 is provided through the side of the sprocket or roller carrying assembly 250 to permit grease to be pumped under pressure into a grease receiving cavity 274 that is located beneath counterbore 270. A grease seal 271 is provided to keep the grease from escaping between the piston 220 and the sprocket or roller carrying assembly 250 as it is pumped into the grease receiving cavity 274.
To remove slack in the tram chain 258, the sprocket or roller carrying assembly 250 is forced to slide within nose piece 215 by pumping grease under pressure into the grease receiving cavity 274. As the grease enters grease receiving cavity 274, the sprocket or roller carrying assembly 250 is forced to slide along the piston 220 carrying with it the idler sprockets or rollers 256. The grease is pumped into the grease receiving cavity 274 until the idler sprockets or rollers 256 have moved far enough into the tram chain 258 to eliminate the slack therein. Thereafter, pieces of shim stock 280 are positioned along piston 220, as shown in FIG. 2, to fill in the resulting gap or shim cavity 218 between the nose piece 215 and the sprocket or roller carrying assembly 250. Each piece of shim stock 280 is U-shaped and has a bore 282 and an opening 284 therethrough to enable it to slide over piston 220 (see FIG. 5). As most particularly shown in FIG. 2, the shim stock 280 may be provided in various thicknesses so that a number of different pieces of shim stock 280 must be combined to achieve the overall thickness necessary to fill in the gap 218 between the sprocket or roller carrying assembly 250 and nose piece 215. After the desired amount of shim stock 280 has been positioned between nose piece 215 and sprocket or roller carrying assembly 250, the shim stock 280 is held in place by a shim retaining plate 286. As shown in FIGS. 2 and 6, the shim retaining plate 286 has a slot 288 in one end thereof that is adapted to slide over a T-shaped retaining pin 224 located on the top of piston 220. The shim retaining plate 286 is secured in position by a screw 290 that is inserted into an aperture 289 located in the end of the shim retaining plate 286. The screw 290 extends through the aperture 289 and is threadedly received in a threaded bore 292 located in the crawler 212. In an effort to keep the screw 290 from backing out of threaded bore 292 during the operation of the crawler 212, a lock washer 294 is often employed. Other methods of securing the shim retaining plate 286 to the nose piece 215, such as pins and cotter key arrangements, have also been used. To complete the process, the grease is permitted to exit out of the grease receiving cavity 274 through the grease passage 273 by removing the grease pumping source.
In another prior design (not shown), a hydraulic cylinder having a piston slidably disposed therein is operatively positioned between the nose piece of the crawler and the sprocket or roller carrying assembly. As with the design discussed above, the sprocket or roller carrying assembly is slidably received in the nose piece of the crawler. To adjust the position of the idler sprockets or rollers, grease is pumped into the hydraulic cylinder causing the piston to slide out of the cylinder and bear against the sprocket or roller carrying assembly causing it to move further into the endless crawler chain. After the sprocket or roller carrying assembly has been moved to the desired position, the grease is then permitted to exit the cylinder to thereby permit the piston to be manually retracted back into the cylinder. Pieces of shim stock are then positioned between the piston and the back of the sprocket carrying assembly to mechanically retain the sprocket carrying assembly in the desired position.
As discussed above, the prior designs have disadvantages in several respects. In particular, the prior designs utilize shim stock to provide a positive mechanical stop for the sprocket or roller carrying assembly. However, as the crawler pads engage and tram across the mine floor, dirt tends to build up in and around the shim cavity due to its relatively close proximity to the mine floor. This build up of dirt makes it difficult to insert and remove the shim stock and thereby increases the amount of time needed to adjust the sprockets or rollers. Often times, before additional shim stock can be added, the entire shim cavity must be cleaned.
Another serious problem associated with the prior designs is caused by the vibration and abuse the take-up mechanism experiences as the crawler changes directions and encounters irregularities in the mine floor. More specifically, the shim retaining plate often becomes loose or falls out of position causing the shim stock to fall out of the shim cavity and become lost or damaged. Depending upon the amount of chain slack present, an abrupt loss of the shim stock could cause the chain to track off the sprockets or rollers causing damage to other portions of the mining machine or conveyor.
Yet another inherent problem encountered with the prior designs is that an inventory of shim stock of various thicknesses must be maintained in the mining area so that adjustments may be made to the sprockets or rollers as needed. Often times the mine mechanic must search for a piece of shim stock with the proper thickness before adjustments to the chain sprockets or rollers may be undertaken. Additional problems arise when there is no shim stock available to make the necessary adjustments. Experience has shown that such composite combinations of a number of shims of various thicknesses and sizes are more susceptible to being jarred out of the shim cavity and becoming lost during the mining process. Also, the mechanic may be precluded from making very precise adjustments to the sprockets or rollers because shims of the proper thickness are not available. As such, under the prior design, less than optimum adjustments for chain slack are frequently made because shim stock having the desired thickness is not available when needed.
Thus, there is a need for a take-up device for removing the slack from endless tram chains used on continuous mining machines and conveyors that can easily be precisely adjusted and maintained without the use of shim stock or similar materials.